Chapter 4

Internetworking

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Outlines
2

● Introduction
● Internetworking with TCP/IP
● Intranet, Extranet and Internet
● IP Addressing
● Subnetting
● Network Applications – Web, Mail, DNS, DHCP

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Introduction
3

● Inter-networking implies networking of networks.

● It is routing of data based on decisions and
agreements reached by the administrations of the
networks involved.
Why networking?
● To meet the critical user needs like sharing data.
● To connect the relevant networks together that can
be shared data among users.

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Cont’
4

Ethernet
⚫ It is the most widely-installed local area network ( LAN)

technology.
⚫ Specified in a standard, IEEE 802.3.

⚫ An Ethernet LAN typically uses coaxial cable or special

grades of
twisted pairs wires.
⚫ Ethernet is also used in wireless LANs.

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Cont’
5

Intranet
⚫ An intranet is a computer network that uses Internet

Protocol(IP) technology to share information within an

organization.
⚫ Sometimes, the term refers only to the organization's

internal website, but may be a more extensive part of the

organization's information technology infrastructure.
⚫ Composed of multiple local area networks.

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Cont’
6

Extranet
⚫ It is a private network that uses Internet technology and the

public telecommunication system.

⚫ This is to securely share part of a business's information or

operations with suppliers, vendors, partners, customers, or

other businesses.
⚫ An extranet can be viewed as part of a company's

intranet that is extended to users outside the company.

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Cont’
7

Internet
⚫ Internet is a global system of interconnected
computer networks that use the standard internet
protocol
suit (TCP/IP) to serve several billion users worldwide.
⚫ It is a network of networks that consists of millions of private,

public, academic, business, and government networks.

⚫ A network between organizations.

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Cont’

08/22/2022 8 8
How to use the Internet ?
9

There are ways to use Internet:

⚫ E-mail

⚫ Research

⚫ Shopping

⚫ News

⚫ Games

… etc.

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Internet Terms? 10

⚫ WWW- The World Wide Web

⚫ Mail

⚫ Browser

⚫ Search Engine

⚫ URL

⚫ Domain

⚫ html

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Cont’
11

Web
⚫ The World Wide Web (WWW), commonly known as the

Web, is an information system where documents and

other web resources are identified by URL(Uniform
Resource Locators ).

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Cont’
12

Mail
⚫ Electronic mail, e-mail or email is an information stored

on a computer that is exchanged between two users over

telecommunications.
⚫ It is a message that may contain text, files, images, or other

attachments sent through a network to a specified party.

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Cont’
13

Browser
⚫ Software program that allows a person to view WWW

documents.

Example

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Search Engine
14

⚫ A web site that will help you search the Internet for key
words, subjects, etc.

Example

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 URL
15

⚫ URL : stands for Uniform Resource Locator.

⚫ The unique address of any web page.

⚫ It tells your computer where the information is stored so

it can be viewed.
Example:
https://[www].[facebook.com]/ [Learn-the-Net -330002341216]/

Sub domain
Protocol Domain
path/directory

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Domain
16

⚫ A way to indicate what type of site you may be viewing.

⚫ Some common domains are:

 .com: commercial,
 .org: non-profit and research organizations
 .gov: government agency
 .edu: education.

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html
17

⚫ The Language used to create

Web Pages.

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 Internet Protocol (IP)
18

⚫ The Internet Protocol (IP) is a protocol used for

communicating data.

⚫ IP is the primary protocol in the Internet Layer of the

Internet Protocol Suite and has the task of delivering

packets from the source host to the destination host
based on their addresses.

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 Cont’
19

⚫ The first major version of addressing structure, now referred to

as Internet Protocol Version 4 (IPv4).

⚫ It is still the dominant protocol of the Internet.

⚫ The packet transmitted by the sending computer may pass

through several LANs or WANs before reaching the destination

computer.

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IP Addressing
20

⚫ Usually, computers communicate through the Internet.

⚫ For this level of communication, we need a global addressing

scheme.
⚫ We use the term IP address to mean a logical address in
the network layer of the TCP/IP protocol suite.

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IPv4 Addresses
21

⚫ An IPv4 address is a 32-bit address that universally defines

the connection of a device to the Internet.

⚫ IPv4 addresses are unique and universal.

⚫ They are unique in the sense that each address defines one

and only one connection to the Internet.

⚫ Two devices on the Internet can never have the same address

at the same time.

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Address Space 22

⚫ A protocol such as IPv4 that defines addresses has an address

space.
⚫ An address space is the total number of addresses used by the

protocol.
⚫ If a protocol uses N bits to define an address, the address space

is 2N because each bit can have two different values (0 or 1) and

N bits can have 2N values.

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 Cont’ 23

⚫ IPv4 uses 32-bit addresses, which means that the address space

is 232 or 4,294,967,296 (more than 4 billion).

⚫ This means that, theoretically, if there were no restrictions,

more than 4 billion devices could be connected to the Internet.

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Notations
24

There are two IPv4 address notations :

⚫ Binary Notation

 In binary notation, the IPv4 address is displayed as 32 bits.

 Each octet is often referred to as a byte.
 Each octet have a value between 0 and 255
 So it is common to hear an IPv4 address referred to as a 32-bit
address or a 4-byte address.

Example: 01110101 10010101 00011101 00000010

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Cont’
25

⚫ Dotted-Decimal Notation

 To make the IPv4 address more compact and easier to read,

Internet addresses are usually written in decimal form with
a decimal point (dot) separating the bytes.
 The following is the dotted-decimal notation of the above
address:
117.149.29.2

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Cont’
26

Example
⚫ Dotted-decimal notation and binary notation for an IPv4

address.

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08/22/2022 27
Example 1
Change the following IPv4 addresses from binary
notation to dotted-decimal notation.

Solution
We replace each group of 8 bits with its equivalent decimal number
and add dots for separation.

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Example 2
Change the following IPv4 addresses from dotted-
decimal notation to binary notation.

Solution
We replace each decimal number with its binary equivalent

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08/22/2022 30
Example 3
Find the error, if any, in the following IPv4 addresses.

Solution
a. There must be no leading zero (045).
b. There can be no more than four numbers.
c. Each number needs to be less than or equal to 255.
d. A mixture of binary notation and dotted-decimal
notation is not allowed.
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Classful Addressing 27

⚫ IPv4 addressing is used the concept of classes.

⚫ This architecture is called classful addressing.

⚫ In classful addressing, the address space is divided into five

classes:
 Class A: addresses are used for larger networks
 Class B: for medium networks
 Class C: for small networks
 Other classes – D and E, are used for multicasting and
research purposes.

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Network ID and Host ID
28

⚫ An IP address in class A, B, or C is divided into network ID and

host ID.
⚫ These parts are varying lengths, depending on the class of the
address.
⚫ In class A, one byte defines the network ID and three bytes
define the host ID.
⚫ In class B, two bytes define the network ID and two bytes
define the host ID.
⚫ In class C, three bytes define the network ID and one
byte
defines the
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Cont’
29

⚫ The first bit of a Class A address is always 0.

⚫ With that first bit 0, the lowest number that can be

represented is 00000000, decimal 0.

⚫ The highest number that can be represented is 01111111,

decimal 127.

⚫ The numbers 0 and 127 are reserved and cannot be

used as
network addresses.
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Cont’
30

⚫ Any address that starts with a value between 1 and 126 in the

first octet is a Class A address.

⚫ Example: 98.56.82.30

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Cont’
31

⚫ The first two bits of a Class B address are always 10.

⚫ The lowest number that can be represented is 10000000,

decimal 128.

⚫ The highest number that can be represented is 10111111,

decimal 191.

⚫ Any address that starts with a value between 128 and 191 in

the first octet is a Class B address.

⚫ Example: 167.3.27.30
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Cont’
32

⚫ The first three bits of a Class C address are always 110.

⚫ The lowest number that can be represented is 11000000,

decimal 192.

⚫ The highest number that can be represented is 11011111,

decimal 223.

⚫ Any address that starts with a value between 192 and 223 in

the first octet is a Class C address.

⚫ Example: 192.168.0.1
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Example 4
Find the class of each address.
a. 00000001 00001011 00001011 11101111
b. 11000001 10000011 00011011 11111111
c. 14.23.120.8
d. 252.5.15.111
Solution
a. The first bit is 0. This is a class A address.
b. The first 2 bits are 1; the third bit is 0. This is a class C
address.
c. The first byte is 14; the class is A.
d. The first byte is 252; the class is E.

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Network Addresses
33

• When an organization is given a block of addresses, the

organization is free to allocate the addresses to the devices

that need to be connected to the Internet.
• The first address is called the network address and defines

the organization network.

• It defines the organization itself to the rest of the world.

• The first address is the one that is used by routers to direct

the message sent to the organization from the outside.

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Cont’
34

⚫ IP addresses, like other addresses or identifiers we

encounter these days, have levels of hierarchy.
⚫ For example, a telephone network in Ethiopia has
three levels of hierarchy.
⚫ The leftmost three digits (+251) define the country
code, the next three digits (058, for example) define
the area, the last seven digits (2212541, for example)
define the subscriber number.

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IP addressing: Summary
35

in binary notation In decimal notation

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Reserved IP addresses
36

⚫ Certain IP addresses are reserved and cannot be used to

serve as an address to a host. These are:

i. Network address:
⚫ Used to identify the network itself.

⚫ Assume a class C network which starts with 200.150.56.

⚫ Hosts can be assigned addresses from

200.150.56.1 to 200.150.56.254
⚫ The address 200.150.56.0 is called
the network address.
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How many networks are there?
37

08/22/2022 43
 Cont’
38

ii. Broadcast address

⚫ Used for broadcasting packets to all the devices on a network.

⚫ Hosts use broadcast addresses to send data to all hosts in a

network.

⚫ Assume a class C network with a network address

200.150.56.0

⚫ The broadcast address for this network is 200.150.56.255

Note:
• Network addresses have all zeros for the host portion.
• Broadcast addresses have all ones for the host portion.
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 Subnetting
39

⚫ To efficiently manage IP addresses, all classes can be

subdivided into smaller subnetworks or subnets.

⚫ This process is known as subnetting.

Advantages:
 Reduced network traffic
 Optimized network performance
 Simplify management

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The subnetting process
40

⚫ To create the subnetwork structure, host bits must be

reassigned as network bits which is often referred to as

borrowing bits.
⚫ The starting point for this process is always the
leftmost
host bit.
⚫ Subnet addresses include:

⚫The Class A, Class B, and Class C network portion,

a subnet field and a host field.

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Cont’
41

⚫ The subnet field and the host field are created from the

original host portion of the major IP address.

⚫ This is done by assigning bits from the host portion to the

original network portion of the address.

⚫ Subnets have subnetwork ID (subnet ID) just as networks

have network IDs.

 Subnet IDs - put all 0’s in the remaining host field.

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 How many bits should we borrow?
42

⚫ To determine the number of bits to be used, the network

designer needs to calculate:

 How many hosts the largest subnetwork requires and

 The number of subnetworks needed.

⚫ A large number of subnets means fewer hosts

⚫ Total number of subnets is 2^bits borrowed.

⚫ Total number of hosts is 2^remaining host bits.

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 Cont’
43

Example:
⚫ if we borrow three bits from a class C address, total
number of subnets is 8 (2^3) and total number of hosts is
32 (2^5)

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Usable subnets
44

⚫ Among the available subnets, it’s not advised to use the

following two subnets:

 The subnet with all 0’s in the subnet field

 The subnet with all 1’s in the subnet field WHY?

⚫ If the first subnet (all 0’s in the subnet field) is used, then

network and subnet have the same address.

⚫ If the last subnet (all 1’s in the subnet field) is used, the network

broadcast address and a subnet have the same address.

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 Cont’ 45

⚫ Hence usable subnets will be 2^bits borrowed – 2

Example:

⚫ If we borrow three bits from a class C address, total number

of usable subnets is 6 (2^3 - 2)

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Usable hosts
46

⚫ All 0’s in the host field is reserved for subnet address

⚫ All 1’s in the host field is reserved for broadcast address

⚫ Hence the number of usable host addresses is:

2^remaining host bits – 2

Example:

⚫ for 3 bits borrowed, total number of usable

hosts are 30 (2^5 - 2).

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Mask
47

• Although the length of the network ID and host ID (in

bits) is predetermined in classful addressing, we can also

use a mask (also called the default mask).
• A 32-bit number made of contiguous 1s followed by

contiguous 0s.

• The mask can help us to find the network ID and the host

ID.

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Subnet masks
48

⚫ For the subnet address scheme to work, every machine on

the network must know which part of the host address will
be used as the subnet address.
⚫ This is accomplished by assigning a subnet mask to each

machine

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Subnet masks
49

⚫ A subnet mask is a 32-bit value that allows the receiver of IP

packets to distinguish:
 The network portion of the IP address from the
host portion of the IP address.

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Subnet masks
50

⚫ A subnet mask is composed of 1s and 0s where:

 The 1s in the subnet mask- refer to the network or

subnet addresses.
 The 0s in the subnet mask- refer to the host
address.

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Default subnet masks
51
⚫ Not all networks need subnets, meaning they use the
default subnet mask

⚫ Class A - network.node.node.node Subnet mask:

255.0.0.0
⚫ Class B - network.network.node.node Subnet
mask: 255.255.0.0
⚫ Class C - network.network.network.node Subnet mask:
255.255.255.0
⚫ These default subnet masks show the minimum number of
1’s you can have in a subnet mask for each class.
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Specifying subnets
52

⚫ Example if we borrow three bits from a class C address, the subnet

mask is 255.255.255.224
⚫ Subnets may also be represented, in a slash format.

⚫ For example, /24 indicates that the total bits that were used for the

network and subnetwork portion is 24

⚫ The subnet mask 255.255.255.224 in slash format is /24

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Subnetting Class C addresses - Example 1
53

⚫ Let us subnet the network address 192.168.10.0 with a subnet

mask 255.255.255.192 or in slash format /26

i. How many subnets do we have?

Since 192 is 2 bits on (11000000), the answer would be 2^2 =

4

ii. How many hosts per subnet do we have?

We have 6 host bits off (11000000), so the answer would be

2^6 = 64 hosts

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Cont’
54

iii. What are the subnet IDs?

⚫ We vary the borrowed bits (00, 01, 10, 11).

 So the subnets are 192.168.10.0, 192.168.10.64, 192.168.10.128,

192.168.10.192

iv. What are the valid or usable subnets?

⚫ The ones which do not have all 0’s or all 1’s in the subnet field,

namely 192.168.10.64 and 192.168.10.128

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 Cont’
55

v. What’s the broadcast address for the valid

subnets?
⚫ The valid subnets start with 01 and 10.

⚫ The broadcast address for these two addresses will have

01111111 and 10111111. Which are 127 and 191.

So the broadcast addresses will be

192.168.10.127 and 192.168.10.191.

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 Cont’
56

vi. What are the valid hosts?

⚫ These are the numbers between the subnet ID and

broadcast address. The hosts for the first valid subnet are
192.168.10.65, 192.168.10.66, …, 192.168.10.126
⚫ The hosts for the second valid subnet are 192.168.10.129,

192.168.10.130, …, 192.168.10.190

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Calculating class A and B networks
57

⚫ The Class A and B subnetting procedure is identical to the

process for Class C, except there may be significantly more

bits involved
⚫ The available bits for assignment to the subnet field:

⚫ in a Class A address is 22 bits.

⚫ Class B address has 14 bits.

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Subnetting Class B addresses – Example 1
58

172.16.0.0 = Network address

255.255.192.0 = Subnet
mask
i. How many Subnets?
Ans: 2^2 – 2 = 2.
ii. How many Hosts per
subnet?
Ans: 2^14 – 2 = 16,382. (6 bits in the second octet, and 8 in
the fourth)
iii.Subnet IDs of valid subnets?
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Cont’
59

iv. Broadcast address for each subnet and valid hosts?

Ans: Below is the two subnets available and the address of each:

Subnet 172.16.64.0 172.16.128.0

First host 172.16.64.1 172.16.128.1
Last host 172.16.127.254 172.16.191.254
Broadcast 172.16.127.255 172.16.191.255

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Subnetting Class A addresses – Example 1
60

10.0.0.0 = Network address

255.255.0.0 (/16) = Subnet mask
i. Subnets?
Ans: 2^8 – 2 = 254
ii. Hosts?
Ans: 2^16 – 2 = 65,534
iii. Valid subnets?
Ans: 10.1.0.0, 10.2.0.0, 10.3.0.0,
…, 10.254.0.0
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Subnetting Class A addresses – Example 1
61

iv. Broadcast address for each subnet and valid hosts?

Subnet 10.1.0.0 … 10.254.0.0
First host 10.1.0.1 … 10.254.0.1
Last host 10.1.255.254 … 10.254.255.254
Broadcast 10.1.255.255 … 10.254.255.255

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 Network Address Translation (NAT)
62

• More hosts to be connected to the internet & IP addresses are in

depletion.

Solution: NAT (used in router).

• Preserve the limited amount of IPV4 public IP addresses.

• NAT translates a set of IP addresses in to another set of IP

addresses.
 Translate from private IP address to public IP address.

Compare and contrast Private and Public IP address!?

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IPv6
ADDRESSES 63

⚫ Despite all short-term solutions, address depletion is

still a long-term problem for the Internet.

⚫ This and other problems in the IP protocol itself have

been the motivation for IPv6.

⚫ An IPv6 address is 128 bits or 32 hexadecimal digits

long.

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 ...’’’
64

Note:
 Computers understand numbers and can be identified by IP

address.
Names are easy to memorized by users instead of numbers.

How to mediate them?

When an IP address is assigned manually, IP conflict!

How to solve this problem?

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DNS server (domain name system)
65

⚫ DNS is an Internet service that translates domain names into

IP addresses.
⚫ Because domain names are alphabetic, they're easier to

remember.
⚫ The Internet however, is really based on IP addresses.

⚫ Every time you use a domain name, therefore, a DNS

service
must translate the name into the corresponding IP
address.

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Cont
66

⚫ Humans are identified with names

⚫ Computers are communicated each other not by names

rather they used numbers(IP address).

⚫ To solve the gap between humans and computers, DNS is

developed.
⚫ It resolves names to numbers(domain names to IP

addresses).

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Cont
67

Example: the domain name www. facebook.com might

translate to 192.168.1.3
 A computer knows IP address 192.168.1.3 is for
facebook.com
 if some one want to use facebook.com, it is difficult
to memorize this IP address.
 So, the domain name (facebook.com) is used and the
DNS
server resolves it as a number.
 This is done by searching the equivalent IP address of the
08/22/2022 73
domain name from cache memory.
Dynamic Host Configuration Protocol (DHCP)
68

⚫ DHCP is a protocol for assigning dynamic IP addresses to

devices on a network.
⚫ With dynamic addressing, a device can have a different IP

address every time it connects to the network.

⚫ In some systems, the device's IP address can even change
while
it is still connected.
⚫ DHCP also supports a mix of static and dynamic IP
addresses.

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Cont’
69

⚫ Every computer on a network must have IP address.

⚫ Two ways of assigning an IP address:

Static IP
⚫ A user assigns an IP address
manually
 IP address is unique for each device
 If manual, IP conflict will happen

Solution: Dynamic IP

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Cont’
70

⚫ Dynamic IP addressing is where a computer gets an

IP address from a DHCP server.

⚫ A DHCP server automatically assigns a computer:

 IP address
 Subnet mask
 Default gateway
 DNS server

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Cont’
71

Lease
⚫ DHCP server assigns IP address as a lease.

⚫ Lease is amount of time an IP address is assigned to the

computer.
⚫ It help to make sure the DHCP server does no run out of IP

address.
⚫ When the lease is expired, the computer send a signal to

renew the IP address lease

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08/22/2022 78